However we can use the nice command to start process with a different nice value, as a regular user, you can not start process with a negative nice value, but you can have value larger than 0.
The structure of the nice is the following:nice -n <nice-value> <command to run>
And it will run the command and give the process a nice value of <nice-value>.
For example, we can start the sleep command with a nice value of 10.

As we can the second sleep, that was started with the nice command, has a nice value of 10.

We can use renice to change nice value of running process, as regular user, we can only increase the nice value, but root user can decrease the nice value.
The structure of the renice command is the following:renice -n <nice-value> <process-id>
For example, we will run sleep command with a nice value of 5 and then use renice to change the value to 10: